1. Field of the Invention
The present invention relates to a method for forming, from a metal plate, a tubular product with a thickened flange portion, combined dies for a press apparatus, and a three axis press apparatus.
2. Description of Related Art
Japanese Un-Examined Patent Publication 2001-1060 discloses a method for forming a tubular product with a thickened flange portion from a metal plate (blank), wherein the metal plate is rested on a die of a circular conical shape and is subjected, as a first stage metal working, to a drawing by a punch. The drawing is ceased under a condition that the flange portion of the blank is still stayed on a circular conical surface of the circular conical shaped die, so that an semi-finished product of a cup shape having an inclined flange portion is obtained. The cup shaped semi-finished product is, then, subjected to a second stage metal working, wherein the inclined flange portion of the cup shaped semi-finished product blank is pressed, thereby obtaining a final product with a leveled flange portion of an increased thickness. In this prior art, a several percent increase in the thickness of the flange portion over the thickness of the blank plate is obtained. Namely, during the execution of the draw forming, an elongation is occurred at a portion of the material contacting with the punch, thereby reducing the thickness. However, at the end of the material contacting with the circular conical surface of the conical die, a reduction of the diameter is occurred, which causes the thickness to be increased over the wall thickness of the blank. However, in the prior art, a subsequent flattening of the inclined flange portion is done, which causes the outer diameter to be relatively increased. Due to the increase in the diameter by the flattening, some kind of thinning is occurred at the flange portion. Thus, a finally obtained increase in the wall thickness of the flange portion is limited to a several percent over the wall thickness of the blank. Therefore, in order to obtain a flange portion of an increased wall thickness exceeding several percent of the wall thickness of a blank, a combined process is essential, where a separate flange member of a desired wall thickness is prepared and a welding of separate flange member is done, resulting in a substantial increase in a production cost.